482 -WEBER ON THE NATURE OF DIAMAGNBTISM. 



supposes in an electro-magnet a constant galvanic current. But 

 on the other hand, the conductor upon which the bismuth 

 is to act must have a fixed immutable position to that magnet, 

 so that it incloses the space in an annular form, in which the 

 bar of bismuth has to be brought in order to produce in it the 

 diamagnetic distribution by the influence of the magnet. That, 

 lastly, the current induced by the bismuth can be observed by 

 continuing the two extremities of the above annular conductor, 

 and connecting them with the ends of the multiplier of a sensi- 

 tive galvanometei', requires no further explanation. 



But with respect to the power of this current induced by the 

 bar of bismuth, it may readily be estimated a priori how small 

 it will be if we consider how feeble the diamagnetic forces are in 

 comparison to the magnetic forces of the iron substituted for the 

 bismuth. On further examination, it results that the induced cur- 

 rent must be so feeble that it can no longer be observed if all the 

 conditions do not act together most favourably for the object. 



The following arrangements were made to attain this end, viz. 

 to induce galvanic currents in a neighbouring conductor by the 

 diamagnetization of the bismuth, and thus actually to observe the 

 induced currents. An iron nucleus 600 millimetres in length, 

 coated several times ^ith thick copper wire, was used as electro- 

 magnet. To the circular terminal surface, 50 millimetres in 

 diameter, of this iron nucleus was fixed the annular conductor, 

 which consisted of copper wire 300 metres long and § millimetres 

 thick, well spun with silk, and coiled upon wooden cylinders. 

 The space included in this annular conductor, in which the bar 

 of bismuth was to be placed, was 140 millimetres in length and 

 15 millimetres in breadth; the bar of pure precipitated bismuth 

 Mas somewhat thinner. The extremities of the annular con- 

 ductor were connected with a commutator, as were also the 

 extremities of the multiplier of a very sensitive galvanometer, 

 the magnet-needle of which was provided with a mirror in which 

 the image of the distant scale was observed by a telescope di- 

 rected towards it. The galvanometer was moreover provided 

 with so effective a damper that it was scarcely possible to ob- 

 serve any vibration of the needle. 



Now whilst a very powerful and constant galvanic current 

 passed through the thick wire of the electro-magnet, the bar of 

 bismuth was withdrawn from the annular conductor in which it 

 was situated, the commutator changed, and the bar of bismuth 



